The invention concerns a compression handle for securing a dental root-canal instrument in accordance with the preamble to claim 1.
The compression mechanism in a known handle of this type (German Patent No 929 867) consists of the segmented jaws of a chuck that a nut can be screwed onto in order to exert radial pressure. Because strength requires that the jaws not be too slender it is necessary to screw the nut on very tightly, which is usually impossible manually, in order to deform them and secure the instrument. A tool is also needed to release a nut that has been tightened to such an extent. Furthermore, building jaws and a threaded cone onto such a relatively small piece is expensive of time and money. Another compression grip (German Patent No. 2 703 637) has a special compression disk between a compression surface on the face of the chuck and another compression surface on a screw-on cap for securing the instrument, a disk that tilts toward the shaft of the instrument and compresses it in place as the threaded mechanism is tightened. It is, however, difficult to manufacture such a relatively small compression disk because even small variations in tolerance can affect its function. Furthermore, since a certain amount of automatic compression frequently occurs during the untensioned state, it is often impossible to subsequently correct the length of the instrument smoothly. It has also turned out in practice that the small compression disk gets lost when the handle is disassembled.